Production of producer gas



Dec. 5, 1933. J. A. MACDONALD PRODUCTION OF PRODUCER GAS Iz @ande y 07 Original Fled'June 30,'1950 A TTOR/VEY Patented Dec. 5, 1933 UNITED s'rATi-:sY

PRODUCTION OF PRODUCER GAS James Alexander Macdonald, Nakuru, East Africa Original application June 30, 1930, Serial No.

465,018, and in Great Britain July 29, 1929. Divided and this application August 11, 1932.

Serial No. 628,427

4 Claims.

This invention relates to the production of combustible gases (which will hereinafter be reierred to as producer gas) by reacting on fuels with air and water vapour under heat, and has 5 for its object to provide an improved method therefor.

In use, the producer gas may be cooled and dehydrated, as Well as cleaned, by any of the usual suitable means, but it is a further object of the invention to provide an apparatus which will deliver a producer gas of good quality together with Water in a state adapted to be fed directly to an engine without previous dehydration.

The invention rests principally upon the three following considerations:-

(l) It is possible to maintain an incandescent zone Within a producer so hot that Water nds great diiiiculty in extinguishing it provided that the reaction is directly supplied With air or oxy- 1 20 gen under a forced draught, as, for example, by

admitting the air through a pipe of restricted diameter that causes it to move with considerable velocity.

(2) Such a reaction zone tends to become very hot and to spread; but it can be kept cool and coniined to a limited volume by surrounding it With a comparatively cool atmosphere of a noncombustible e. g. steam.

(3) It is an advantage to supply H2O to the reaction in the form of iiuid and not of gas, i. e. water not steam, if this can be done satisfactorily Without extinguishing the tire; because the specific gravity of v vater is over 1,000 times greater than that of steam and a suflicient Vquantity of H2O can be injected Without interfering with the adequacy or accessibility of the oxygen for combustion. Moreover the cooling eiectof a given Weight of iiuid so vastly exceeds thatlof Vcress section diagrammatic representations of a an equivalent of steam that the tendency to spread is correspondingly more easily checked.

. The preferred form of apparatus for carrying out the invention primarily comprises a producer gas plant Yhaving a combustion chamber of substantial volume, a bottom adapted to hold Water up to a certain level, an air inlet pipe of restricted diameter extending Within said chamber and adapted to create an incandescent zone of limited volume and hightemperature at or adjacent the delivery end thereof, and means to 50. deliver a supply of Water on to said incandescent zone. Y

The apparatus forms the subject of a copending patent application No. 465,018.

As will hereinafter appear, a substantial volume of water vapour is created and` maintained Within the body o f the chamber, the localized incandescent zone being surrounded by an atmosphere of said vapour and the primary products of the reaction beingY immediately cooled by it and fixed and delivered in their original state Without the occurrence of serious secondary reactions. Further, the Walls of the chamber are maintained much cooler than is usual in such plants even after prolonged use.

The producer gas may be delivered with an amount of Water vapour (Whether in a free state or not) which considerably exceeds normal practice, and at a temperature below 100 C. If dried, it discloses on analysis a producer gas of good quality; but it is also readily capable of direct use without drying.

The invention is applicable for use with solid fuel such as coal or charcoal, or with liquid fuels. In the former case, the height of the inlet pipe above the bottom must be sufficient to provide for the accumulation of a certain amount' of ash.

The outlet pipe is preferably situated oppo` site and slightly above the inlet pipe, and its penetration Within the chamber is preferably adjustable to provide means for controlling the reaction. l

The apparatus as described may be coupled directly to an internal combustion engine with the interposition of nothing more than any simple device for extracting particles of solid carbon, and when a steady, Working condition has been reachedjthe nature of the products is determined by the amount of Water supplied by means ofV the inletl pipe and the degree of penetration of the outlet pipe Within the chamber.

The invention is illustrated in the accompanying drawingin which Figures 1 and 2 show in vertical and horizontal plant arranged for use in accordance with the invention and intended for use with charcoal.

In the form illustrated, the plant comprises a cylindrical preferably metallic chamber 1 having an upper closure 2 for the insertion of fuel. rihe inlet pipe 3 penetrates adjustably within 100 the chamber as shown, and a spray 4 is arranged to direct a finely-divided jet of Water through the inlet pipe on to the incandescent Zone as high up as possible. Where the draught is sufficiently forced, a drip of water will be suitably broken up and whirled in by the rush of air.

xThe outlet pipe 5 is adjustably mounted in the .opposite Wall of the chamber coaxially with the pipe 3. Its penetration Within the chamber may be extended to the points indicated in dotted lines. It is arranged slightly higher than theinlet to avoid its being flooded.

The inlet pipe 3 is arranged as low as convenient for the accumulation of ash, and to provide an overow for any water collecting in the bottom of the chamber, without being sufficiently high to have much waste fuel below the re.

In operating such a plant, the nre is nrst lit, e. g. by applying a lighted torch to the pipe 3, and when combustion is satisfactorily established, water, at rst in small quantities, isinjected through the spray 4. Circulation is effected by applying pressure to the pipe 3 or, preferably suction to the pipe 5.

From an examination of the temperature of the walls of the container during warming up and running, it would appear that when a steady condition has been reached the ame is confined to an'inner space which may correspond probably to that indicated at 6, the hottest part of the name where combustion of the fuel principally takes place being indicated at 7, and 8 indicating the inner Zone where no combustion takes place.

The actual incandescent zone probably varies in volume slightlyfrom time to time in accordance with engine demand and/or rate' of air supply. The reaction Zone may be regarded as being bounded by a pulsating flexible envelope e. g. that within the isotherm 10. When the water vapour reaches the isotherm 9, the reac tion extracts fromit part which is sufcient for its own continued propagation. In general, the water on entering is instantly converted into jets of vapour which expand outwardly in all directions away from the reaction zone with semiexplosive force. These vapour jets enter into the outer reaction zone and also help to form the roughly concentric enveloping zone about the reaction zones and maintain the surrounding atmosphere of water vapour against condensation losses Sac. Another part of the water falls into the pan-like bottom where a certain amount is constantly evaporated and helps to envelop the underside of the incandescent zone. Further, the zones of equal temperature under steady conditions appear tocorrespond generally with the isothermals shown at 9, 10, 11, 12. It is believed that the isothermal '7 represents roughly the zone of reaction between the oxygen of the air and the carbon of the charcoal to produce carbon dioxide: that the isothermal 6 represents the zone of reduction to carbon monoxide: the isothermal 9 that where steam enters into reaction with the carbon to produce carbon monoxide and hydrogen. The two latter reactions absorb heat and the whole of the reaction zones are surrounded by a roughly concentric envelope of vapour roughly represented by the isothermal 10. A body of current of water vapour is thus positioned between the edge of the flame 6, and the right-hand wall of the chamber in Figure 1, so that even at the lowest part of the chamber the temperature of the wall does not exceed a value which can be withstood by metal, and it is not necessary to use nre-brick or any special lagging. The temperature at the central part of the top underneath the closure 2 remains hotter than the temperaure in other parts of the roof which is all more or less a cloud Zone with descending rain, and the temperature of the left-hand wall in Figure 1 is hottest about 'one-third or onequarter way down, the temperature immediately above the outlet pipe 5 remaining substantially cool. It will be appreciated that with a given demand on a chamber of iixed size, the contributory factors which together determine the exact size and position of the flame are the size of fuel, the diameter and intrusion of both inlet and outlet pipes, and the amount of water supplied.

Under suction the air is supplied to inlet pipe 3 at atmospheric pressure, the end of the pipe being merely left open. The diameter of pipe 3 is sunciently restricted to ensure that the air moves therethrough with substantial velocity under the suction applied to pipe 5 so as to apply air under iorced draught to the incandescent zone. The supply of water, however, is controlled so that excess is always present above the amount normally necessary to the making of good gas. The bottom of the container may be kept wet or even flooded, without the gas becoming debased as would be expected.

With air supplied at substantial velocity and the water projected horizontally as described, it is impossible for the incandescent zone to be extinguished, as the liquid water is so quickly transformed chemically or into steam, or removed from the incandescent zone. Excess of water does not cause any substantial penetration of water or steam into the reaction zone itself (beyond the amount which the reaction requires) since the pressure is much higher at the inner part of the reaction zone, which is the hottest part, than at the boundary. Such excess of water, therefore, only results in slightly restricting the volume of the reaction Zone (isothermal 6) and in adding to the quantity of water in the pan-like bottom.

The steam formed is continually being condensed in the upper part of the producer, falling 110 downwardly through the mass and being either re-converted to steam or reaching the pan-like bottom; but this transformation is insufficient in quantity to quench the flame in the reaction zone.

The amount of water supplied after the bottom -115 has been nodded may be as much as 1 kg. or 11/2 kg. per 1 kg. of charcoal. An actual plant which has given satisfactory results comprises a drum 90 c.m. high and 52 cm. diameter with inlet and outlet pipes 2.5 to 5 c m. This plant will 120 drive a four cylinder automobile engine rated at -20 H. P. at 1100 revolutions per minute, the engine being altered only to provide a compression ratio of about 6 to 1.

In a modification, the plant comprises a cylindrical chamber 180 c.m. high and 6'7 c.m. diameter, the inlet and outlet pipes being 5 c.m. or 7 c.m. diameter. When this plant was coupled to a four-cylinder H. P. engine at 550 revolutions, the consumption was in the region of 32 130 kg. of water per hour. The amount of water supplied when coupled direct to a single cylinder engine designed to give 8 H. P. at 350 revolutions per minute was about 5 kg. per hour, the only adjustment required other than the setting of 135 the spray valve being a variation of the penetration of the` outlet pipe 5 which advantageously should be given a different setting for engines diiering in output by 10 H. P. or more. With this plant the inlet pipe is about '7 cm. above the bottom of the chamber.

By controlling the water'supply and the penetration of the outlet pipe 5 within the chamber, a very delicate control of the operation of the plant is provided: when the plant is, for example, coupled to an internal combustion engine, comparatively slight axial displacement of the outlet pipe 5 produces appreciable variation in thepower output probably owing to the fact that the gases are drawn off from a more suitable zone 150 ofthe total reaction so that an optimum position is readily found for the outlet pipe. After this position is reached, the engine may be controlled in the ordinary way by throttle.

If a plant designed for an engine of given horsepower is utilized with an engine of larger horsepower, the suction in pipe 5 will be increased, and the plant generally will work at higher temperatures. Within reasonable limits, it will, however, respond to the increased power output on increase or^ the amount of water supply through the nozzle 4, and resetting of the outlet pipe 5, and of course more frequent feeding of fuel through the closure 2.

The invention is not confined to the use of solid fuel, as it may be employed with liquid fuels which may be burnt in a similar kind of closed chamber, the liquid fuel being separately injected or applied through the air inlet.

The plant as described above can be operated successfully with oil fuel either by direct injection or by mounting a drip feed device in the upper wall of the inlet pipe 3. The combustion zone in such case is localized by providing a mass ci solid material such as re brick chippings adjacent the end of the inlet pipe.

The said plants can also be operated successfully with soft coal or anthracite in the form of nuts, although in such case a tar-extractor may be required.

In all cases it is important to have a chamber of sufficient volume that the incandescent zone is localized and is entirely enveloped in an atmosphere of water vapour, and that an extended path is provided for the circulation of the Vapour and products of combustion which probably move in zones corresponding in direction to the general direction of the isothermals indicated, the water vapour serving not only to lower generally the temperature oi the outlet gases but also preventing the production of secondary reactions in zones substantially remote from that of the flame 6.

It is very important that all joints of the fuel and ash closures be tightly sealed, and all air leaks into the chamber be avoided, the chamber being completely closed except for the inlet and outlet pipes 3, 5.

With the arrangement described, the incandescent zone remains limited in volume and does not tend to creep up the chamber on prolonged use, probably owing to upper condensation and the movement of the water vapour from the upper part of the chamber towards the outlet D198.

Although the localized incandescent zone may be at 1300" C. or more, it is an advantage of the invention that the temperature round the walls of the container is maintained low so that a metal container of ordinary quality may be employed. The water may be fed through a nozzle arranged above the inlet pipe, so as to deliver the jet on the top of the incandescent zone.

I claim:-

1. A method of generating producer gas consisting in supplying air to a closed firing chamber by means of a restricted inlet to create a highly incandescent zone adjacent to the delivery end of the said inlet, and in delivering on to the said zone water in excess of the reaction requirements to localize the said zone and maintain the base of the chamber wet.

2. A method of generating producer gas consisting in supplying air to a closed chamber by means of a restricted inlet near the bottom thereof to create a very hot zone near the end of the said inlet surrounded by cooler reaction zone, and in projecting water on to the said hot zone in sufficient volume to restrict the said zone by conversion of water into vapor forming an enclosing roughly concentric envelope about the said zone and the cooler reaction zone, and to enter into the reaction in the outer part of the said cooler reaction zone while maintaining the base of the chamber wet.

3. A method of controlling the generation of producer gas in a closed chamber provided with inwardly projecting inlet and outlet by forming reaction zones surrounded by a roughly concentric vapor envelope produced by projecting water toward the hottest zone suiiicient in quantity to leave liquid water outside the reaction zones in excess of the reaction requirements.

4.-. A method of controlling the generation of producer gas in a closed chamber provided with inwardly projecting air inlet and gas outlet by forming reaction zones surrounded by a roughly concentric vapor envelope produced by projecting water toward the hottest zone suicient to leave liquid water outside the reaction zones in excess of the reaction requirements, the inward penetration of the air inlet and the quantity of water supplied being variable.

JAS.ALEX. MACDONALD. n 

